1. Field of the Invention
This invention relates to an optical disk in which address data in pit train are preformatted and a recording and/or reproducing apparatus and method for recording and/or reproducing data for the optical disk.
2. Description of Related Art
Examples of optical disks of the WO (write once) type and the rewritable type include magneto-optical disk and Digital Versatile Disc (DVD)-RAM according to the ISO (International Organization for Standardization) standards. These optical disk records desired data by the sector by referring to the address data recorded in the disk by prepit beforehand. In other words, the sector position can be identified by the prepit header (address).
The case of DVD-RAM will be described here as an example of the formation of prepit header. As FIG. 1A shows, an address area AR2 which will be said prepit header is formed at the head of the sector and the addresses of the groove (groove G) and land (land L) of the following user area AR1 are recorded. The record reproducing apparatus reads this address area AR2, confirms that this is the desired address, and then records or reproduces data to or from the land L/groove G of the user area AR1 following the header.
The pit train of headers on the address area AR2 is disposed in such a way that its center in the radial direction may fall on the prolongation of the boundary between a land L and a groove G. For this reason, the prepit header can be reproduced either on the prolongation of the land L or that of the groove G.
However, the contents of the prepit header themselves are in a similar shape as those of ISO-MO stored only on the groove G (the land L).
In other words, the header HL (header 1 and header 2) of the address area AR2 shows the address of the following land L. And the header HG (header 3 and header 4) shows the address of the following groove G. The header HL and the header HG altogether account for 128 bytes as shown in FIG. 1B.
The details of this value 128 bytes are shown in FIG. 1C. Within the header HL, the header 1 consists of a VFO (variable frequency oscillator) used for PLL phase locking of 36 bytes, an address mark (AM) which is a synchronization signal for headers of 3 bytes, ID of 6 bytes constituted by a physical ID (PID) which takes the form of either a track address, a sector address, a segment address or other ID information of 4 bytes and its parity PED (PID error detection code, EDC) of 2 bytes, and a postamble (PA) of 1 byte added to terminals of modulation. Here, VFO is a consecutive repetitive data pattern for assuring the reproduction of data even when the disk rotation is subjected to any variation. The remaining header 2 of the header HL is composed in the same way as the header 1 except that the VFO contains 8 bytes. In these two headers, a same ID is repeatedly recorded twice. And the header 3 and the header 4 of the header HG have a similar relationship.
The composition with a particular attention paid on the header 1 and the header 2 of the header HL is shown in the following table 1. Each ID is subjected to an EFM (eight fourteen modulation) for each byte, and a recording pattern further subjected to a NRZI (non-return-to-zero inverted recording) modulation forms the pit.
As the modulation mode of ID used in the DVD-RAM is the EFM (eight fourteen modulation) mode, 1 byte=8 bits of ID is modulated into 16 channel bits (ch). Actually, VFO, AM, etc. which are not data arranged by the bit show values converted in the same way as ID. Incidentally, AM and PA are claimed to be unique patterns that cannot be found in EFM.
Due to a shift toward shorter wavelength in laser and higher N/A ratio of the optical system in recent years, efforts have been made to advance towards a still higher density of recording in the user area. As a natural consequence, in redundant preheaders for the user area, a shift towards a higher density is also sought.
At a high density, a defect of the same size will produce a greater effect to data in the user data area AR1 and ID in the address area AR2. And an attempt to promote a shift towards a higher N/A ratio may take the form of a thinner disk substrate in order to secure the skew margin. However, a thinner disk substrate will make the effect of dusts and scratches more remarkable. These defects will cause errors in user data and ID. Since ID is used to manage and control the recording and reproduction of user data, ID errors must be minimized.
In reproducing ID in the address area AR2, it is possible to address to small errors by transforming ID (PID) into error correction codes (PED). However, in view of essentially little information contained as ID, the signal cannot be expanded to a large size, and many errors cannot be corrected. And the presence of any defect in an area used for PLL phase locking (including VFO area) affects the whole header (ID) and can disrupt the process of error correction. This is because, as shown in Table above, generally in the DVD-RAM disk format, the VFO area account for a substantial part of the preheader.
In other words, an ordinary prepit header requires a relatively large VFO area for PLL phase locking as compared with an ID area, and the presence of any defect in an area used for PLL phase locking including the VFO area produces adverse effects on the whole header (ID).
It is therefore an object of the present invention to provide an optical disk capable of eliminating the effects of any defect to the whole header.
It is another object of the present invention to provide an optical disk recording and/or reproducing apparatus rendering the PLL for address demodulation unnecessary and capable of reducing the circuit size.
In one respect, the present invention provides an optical disk in which an address information area having address information recorded therein beforehand and a recording and reproducing area are alternately arranged, wherein an address mark for indicating the start of an area is arranged at the head of the address information area, and the address mark is followed by the address information.
In another respect, the present invention provides a recording and/or reproducing apparatus for recording and/or reproducing data on an optical disk in which an address information area and a recording and reproducing area are alternately arranged including:
a reading means for reading a recorded signal recorded on the optical disk;
a signal processing means for processing the signal read by the reading means in order to read address information;
an address information detecting means for detecting the address information from output processed by the signal processing means in response to a prescribed sampling clock.
Specifically, no clock extracted from the PLL are used, and external clocks are used for sampling. The adoption of this method makes the VFO areas unnecessary.
The recording density of ID is attenuated so that sampling may be possible by using external clocks. The dilution of the ID recording density enables to contain the effects of defects and to minimize errors. The remaining errors will be taken care of by the error correction process. As the disk is eccentric and ID channel bits on the disk and the sampling (external) clock are synchronized, the sampling clock is not on the optimum phase for sampling ID channel bits in the disk. In order to assure a precise phase locking and demodulation even if they are out of phase, the recording density is diluted as described above and moreover the detection of mark/space differences will be used.
And the PE (phase encoding) modulation in which the pit always consists of pairs of mark/space is used. And in order to avoid any phase shift between the sampling clock and ID channel bits from growing larger, edges containing phase information at the center of the pit (bit center of PE) are calculated by difference, and a sampling timing compensation will be performed.
Moreover, according to the present invention, it is possible to eliminate the effects of defects to the whole address area in a high-density optical disk. And an attenuation of density enables to reduce relatively errors due to the effects of defects and the correction of remaining errors enables to reduce errors in reading addresses. Sampling and demodulation can be performed precisely without using PLL.